The association of electricity with medical sciences dates back to the 18th century when Galvani demonstrated that most of physiological processes were accompanied with electrical changes. The electric field generated by the action of nerve and muscle cells constitute bioelectric signal. This chapter discusses various aspects of the electrical signals which are generated from internal sources, namely muscles and nerves. Discovery of micropipette type electrodes, stimulus isolation unit, biostimulators, bioamplifiers, noise attenuators, cathode ray oscilloscope has made possible to see moving impulse of biological origin on screen. Display of signals facilitates a detailed study by specialist. The electrical measurements on cells working in situ are now been made. Discovery of voltage and patch clamping techniques have further enriched over knowledge regarding biopotentials. As the body acts as a volume conductor, these signals can be picked up from the surface of the body or from within and their amplitude changes and wave profile with respect to time can be faithfully displayed and recorded. Clinically important signals that is electrocardiogram, electroencephalogram, electromyogram, electroretinogram, electroocculogram, electronystagmogram have been discussed in this chapter.